Survey of Organic Chemistry
Survey of Organic Chemistry CEM 143
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Date Created: 09/19/15
CEM 143 SUMMER 2009 The following is a reaction summary to help you remember all the reactions that you should know from Chapter 3 ALKENES The following reactions involve carbocation intermediates If you have a symmetric alkenealkyne same thing attached to both ends of the multiple bond then it does not matter where you add the first bond However if the alkenealkyne is unsymmetric then you must add the first bond to the position that leaves the most stable carbocation as the intermediate methyl lt primary lt secondary lt tertiary lt allylic Addition of Hydrogen Halides HX H gt X HX HCI HBr HI HOSOsH H2804 Acidcatalyzed addition of water H H2304 039 H20 4 OH Addition of Halides X2 X gt x H X XCBror CEM 143 SUMMER 2009 12 amp 14 Additions to Conjugated Dienes HX HW gt X X HW HX HCI HBr HI HOSO3H H2804 H2804 H H20 X2 XW X XCBror W IF EXCESS REAGENT ADDED TO THE ABOVE ALL DOUBLE BONDS WILL REACT AS SEEN BELOW 1 l HW OH OH HVgtlt X X Additions to NONConjugated Dienes HX excess HW H gt W X X X X X HX HCI HBr HI HOSO3H H2804 X2 excess 39 X W E XCBror CEM 143 SUMMER 2009 Other Reactions HydroborationOxidation This reaction is the only reaction that adds H and OH in an opposite way ie AntiMarkovnikov H syn addition 8H3 HBlH here BH2 gt gt H Since boron is less 7 electronegative than H202 hydrogen H is now OH the atom that has the magi L partial negative rather H 2 than the normal partial positive charge and boron is partially positive Hydrogenation syn addition rp here H l I Pt surface Multiple Bonds H2Pt W HWH This reaction will ALWAYS H H reduce ALL double bonds present conjugated or not it cannot stop at just one CEM 143 SUMMER 2009 Oxidation Reactions Oxidations of Alkenes OH N KMnO4 OH cool dilute Note that this reaction adds both OH39s to the SAME face of the double bond SYN ozonolysis N 1 03 A O 2 Zn H20 0 V epoxidation 0 JL 0 O R O H AK Remeber that it does not matter what the 39R39 group is on the peroxy acid you still get the same product ALKYNES The reactions of alkynes are VERY similar to alkenes and work essentially the same way The differences are 1 Addition reactions usually do not stop at just one addition and 2 When H and 0H are added a reorganization of the bonds takes place tautomerization For an explanation of these differences see the following CEM 143 SUMMER 2009 Addition of Hydrogen Halides H X HX excess gt a e H X HX HCI HBr HI HOSOsH H2804 Acidcatalyzed addition of water H H N Av Y OH 0 Addition of Halides X2 excess H X 6 X Cl Br or HydroborationOxidation H syn addition here BH3 H B H zk 39 BH2 H H202 0 NaOH H 4 Hz0 OH CEM143 Summer 2009 Chapter 5 Stereoisomerism Types of Stereoisomers All 01 these have the same molecular formula C5H 0 oletrans isomers They differ but are structurally different so in geometry wilh respecl to the they are called STRUCTURAL double band They are called ISOMERS OR CONSTITUTIONAL lSOMERS GEOMETRlC ISOMERS These lwo molecules are These two molcules Cl 039 differ in their conformation a H m lhier position as axial or equitorial so they are H called CONFORMATIONAL ISOMERS Types of Stereoisomers H Cl IQI Br H l MIRROR PLANE These molecules are nansuperimposable mirror images at each other There is no way in 3dimensions you can rotate one and make it look the same as the other These are called CONFIGURATIGNAL ISOMERS Stereocenters Basically considered an atom C for our purposes with 4 different substituents attached to it Enantiomers Mirror image of a stereocenter You can draw one by just switching the position of two adjacent substituents These two molecules are enantiomers Notice that the Br amp are just switched Br H H A 1 Br H Assigning Stereochemistry R amp S designations Assigned by atom priority remember Cahn Ingold Prelog rules Atom with the lowest priority faces away from you R priority rotates clockwise or to the 39right 8 priority rotates counterclockwise or to the Ieft Priority groups Priority groups progress 39 progress clockwise 39Fl39 counterclockwise 39S39 Assigning Stereochemistry What if the lowest priority group isn t pointing away dashed from US Priority groups progress clockwise BUT the group with 4th priority is pointing towards us not away from us so we switch stereo chemistry 39S39 More than one stereocenter Diastereomers molecules that do not differ in all stereocenters at least one stays the samechanges These two molecules are diastereomers How do we know how many possibile stereoisomers there are n number Of stereocenters 2n number of possible stereoisomers So if there are 2 stereocenters n 2 therefore 22 4 Terminology Stereocenter stereogenic carbon chiral center and chiral carbon are often used interchangeably The term chiral infers handedness quot coali coor ri J quot H R R F 39 H NH I IT NH There is another term called optically active that is more specific Optically active molecules can twist planepolarized ightbut how and what does that really mean Polarimeter Used to measure the optical rotation of molecules in solution l I 2 Light Source Fixed polarizer cannot rotate Polarimeter Tube 10 cm long contain optically active substance in solution which causes the plane of polarized light to rotate Analyzer A Rotateable Polarizer This lens is rotated until no light goes through the second lens The angle is then measured to determine the optical rotation of the solution Representations of Molecules CH3 H30 Cl Br H CHzCHs Newman Projection Line drawing showing stereochemistry Br Br CI 9H3 I 6H20H3 CH3 Br H CI CH3 CH20H3 Fisher Projection H CH3 Fisher Projections Cl CH CH3 3 Egt Br H 3quot H CHQCHs k View from bottom Why do we need yet another way to represent molecules Because it makes stereochemistry easier Fisher Projections Diastereomers I I I I CH3 CH3 CH3 ELH Br LH H ELBr LCH3 H3C CI Cl LCHa CH20H3 CH20H3 J Y Enantiomers Enantiomers mirror Images mirror images Chiral Achiral amp Meso Chiral just means that there is stereochemsitry about a bonda chiral center canl rotate plane polarized light Achiral basically means not chiral O Look for symmetry A meso compound is a speci c term for a compound with a plane of symmetry such that the two or more chiral centers cancel each other out are superimposable Another good reason to use a Fisher Projectionit makes it easier to see Example of a Meso Compound Rotate 1 80 CH3 L532Br EL Br CH3 You get back to the identical MIITOI39 Image compound Meso Compound Identification Another good way to identify a meso compound is to see if there is a plane of symmetry through the middle of the molecule Geometric Isomers Revisited We have learned cis and trans thus far for stereochemistry about a double bondBUT 39 This nomenclature is only valid when there are 2 nonhydrogen substituents on the double bond When there are 3 or 4 substituents E amp Z must be used Epoxides Epoxides O A Epoxides are 3membered rings that contain oxygen They are very strained and therefore very reactive How do you make epoxides General Reaction peracid O 2 A General formula of a peracid Like hydrogen peroxide OOH H L These to oxygens make it a R OOxH 39per39 acid rather than just a carboxcylic acid Peracids Peracids you will see A O peracetic acid 0 H mchloroperbenzoic acid mCPBA CI Examples mCPBA W mCPBA O H ICH3 H H30 H Reactions of Epoxides Acid catalyzed ring opening H CH30H 0 H30 OH o A How does it work on H I H HO A B H 0H gt OH O H H Spectroscopy Chapter 12 CEM 143 Summer 2009 Introduction Spectroscopy provides information about functional groups Relies on the chemical environments of atoms as well as the numbers and types of atoms We will learn about 2 types of spectroscopy Infrared Spectroscopy Nuclear Magnetic Resonance Spectroscopy Infrared Spectroscopy Measures frequency at which different types of bonds within a molecule vibrate when moving httpenwikipediaorqwikinfrared spectroscoov Infrared Spectroscopy Low energy long wavelength Measured in wavenumbers om1 szxhle Infrared Spectroscopy 100 if ire O 1165 cmquot 3 JL CH2 wag 0 2705 cm E H H CH2 4 50 ltum snatch quot5 m CH2 1250 mquot g snssnr CH3 mlk 2 2050 cmquot CH2 7 3551 stretch 4 3000 2000 1000 500 Frequency Infrared Spectroscopy The most important regions for you to remember are the ones listed here however you may disregard the fingerprint region CEC CiN c N of 4000 N H O H 3200 2800 2300 2100 1800 1500 Fingerprint i i i i i i i i i i l 2380 I Madman cm 1 4000 3000 C0 2000 nuloi 1000 xrrNurasa rum mu scm x staernrans Frwmrsnacn LIEUID F m J HIT NDHSN 5LnRE I am mum E HDE suanrwnasun x wmwzlam anqu FILH k A f W K Nuclear Magnetic Resonance Spectroscopy NMR Measures the magnetic spin of protons in an atom s nucleus when placed between to very large magnets at very low temperatures Most common is 1H and 13C NMR Identifies UNIQUE carbons or hydrogens Scale is ppm parts per million Carbon 0 200 ppm Hyrogen 0 12 ppm Finding symmetry is the most important step NMR Spectroscopy The tV 0 EH3 groups These two CH3 groups are I en ica H 30 H BC are Identical HZC CHs Br This CH2 group is This CH group is different than the CH3 different than the CH3 groups groups NMR Spectroscopy A H30 CI I3 Here we have 5 3 types of carbons but only 4 types of H2C CH C C hydrogens since carbon 39839 doesn39t All the groups here D D have any hydrogens are different attached to it NMR Spectroscopy H H H H All the carbons are the same here and so are all the hydrogens H H A H CH3 H c B H Here they are not Now we have 4 types of carbons and by extension 4 types of D c hydrogens H H NMR Spectroscopy Br Br Br A Br B A A B A C I B B c i B B B B D C Br A The Concept of Deshielding This is an electron quotcloudquot around the I nucleus Nucleus of If two atoms that have the an atom same electronegativity are bonded together the electron quotcloudquot around each doesn39t change much The atom with the deshielded nucleus can 39feel39 the effects of being in a magnetic field more so than that of the other nucleus and therefore a 39shift39 is seen in the output This shift is to a lower But if two atoms that have different eld h39gher ppm electronegativities are bonded together the electron quotcloudquot around the less electronegative element is pulled away from the nucleusthis is called deshielding the nucleus The Concept of Deshielding In a carbon NMR spectrum these two carbons would appear roughly at the lower end of the ppm scale and would be very close to one another This carbon however would appear at a much higher ppm and is said to be shifted 39downfield39 to a higher ppm because of the fact that is is deshielded by it39s oxygen neighbor w w w w w 180 160 140 120 100 80 usrnnrus ppm 180 usrnxrx47 160 w 140 w 120 w 100 non 80 Br usrnsrzs4 160 w 140 w 120 w 100 non 80 Carbon NMR Shift Table 393 Aldehydes 1LHQ Ketones RQCO I l HHLZCHRI I Rgczcm r 4 F RQCZISHQ I I 0 1402 I I CCl f l C Br C H Satumted Alkanes Aromatics 3 1ng Heteroaromatiss C OH C SR RCOrH Carbonth Acids RCN C OR C Ar 11 00 1139 Esters 1 2 Sl f39oaddes ulfoms R CONRE CR 339 Armdes I l Q 9 C C R l l l I l 200 150 100 50 00 ppm 5 Proton NMR Proton NMR works exactly the same way as carbon NMR but looks at the hydrogens attached to each unique carbon The concept of deshielding also applies here There is one more concept though that we need to discuss Multiplicity Multiplicity is seen in 1H NMR only It shows up as a splitting of a peak What it tells us is how a proton is affected by the others around it or it s nearest neighbors The general rule for multiplicity is n 1 multiplicity where n number of hydrogen neighbors So what are nearest neighbors Multiplicity B So there are 2 nearest H2 neighbor hydrogens A C A following the n 1 rule H C CH the signal for the CH3 3 3 hydrogens should be split into 3this is called a tri let Then these p hydrogens are If I am looking the nearest neighbors at this methyl group39s hydrogens Multiplicity B So there are 6 nearest H2 neighbor hydrogens A C A following the n 1 rule H30 CH3 the Signal for the CH2 hydrogens should be split into 7this is called If I am looking a Septet at this methylene group39s hydrogens Then these hydrogens are the nearest neighbors 1 HVMrann7S Multiplicity Multiplicity Peak shapesplitting follows Pascal s Triangle 1 11 121 1331 14641 15101051 Proton NMR Shift Table I I E Ihers Sul de at 31113318 quot LET CH R H RE Ij I b 4 I I I I I 1 I I l I I I I 39 quot39 211 Math I I A 1I IIhII15 IiI I HIZIHIZZHE1 r I Eff F 1391 3quot3933H 39 Ami H r I E39y FCH IIIH IH I 4 I 4 CI EVE1H I i I I EIJLCH H 39 I I 139IIZi CIH IiZZIEIq ISH I I I I Elmira FLIZZIZZZINH ROH A Fiat1H PhIiIZIH I I I I I I 7 quotj 39339 539 quot339 4393 3 U ll 11 I I 111ujejI I l I 13539 111339 1IIZI 90 3 I O AOH acetic acid HsFruzrms hexane HSVVHXVSX7
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